In electric carpet sweepers with a central drive, a drive wheel is arranged in the mid portion of the channel for accommodating the brushes. Cantilevered shaft portions extend to the left and right of the drive wheel and carry respective brushes as disclosed, for example, in British Patent No. 842,668. If the drive wheel is driven by a flat belt as disclosed in British Patent No. 842,668, the flat belt is deliberately used as a type of coupling since the belt slips when a brush is blocked thereby preventing the motor from becoming destroyed. However, if a toothed belt is utilized in lieu of a flat belt, additional protective measures must be taken to prevent the motor from becoming destroyed since the toothed belt cannot slip under normal conditions.
For this purpose, many known motor protective switches can be utilized. However, these switches are very expensive and, at the onset of the blocked condition, cannot prevent the toothed belt from being intensely loaded for a certain length of time depending upon the switching speed of the switches.